There are currently no effective pharmacological or behavioral treatments for cocaine addiction. One possible explanation is that the neural correlates of drug-seeking are poorly understood. Understanding the neurophysiology of cocaine-seeking may enable the development of treatments aimed at altering the activity of neurons important for generating these behaviors. One brain region critical for cocaine-seeking behavior is the nucleus accumbens (NAcc). Over the past ten years, our lab has found several correlates of cocaine- seeking encoded by single NAcc neurons during drug and drug-free states. However, cocaine addiction is a complicated disorder that is likely encoded by other brain regions. Since most neurophysiological studies were localized to the NAcc there is a paucity of physiological data supporting this assertion. One region likely to encode cocaine-seeking is the ventral pallidum (VP). The NAcc primarily and massively projects to the VP. Similar to the NAcc, VP lesions decrease cocaine-seeking behavior. However, there has been no neurophysiological investigation into the encoding of cocaine-seeking behavior by VP neurons. In order to address this discrepancy, we will simultaneously record NAcc and VP neurons during cocaine-self administration as well as cocaine-seeking following a period of abstinence in which cocaine-associated cues are noncontingently presented. Such data will be important for understanding the role of VP neurons during binge and relapse behavior. Since the vast majority of NAcc projection neurons are GABAergic (e.g., inhibitory), NAcc neuron firing may be inversely related to VP neuron firing. However, recent reports of VP neurons during sucrose-seeking behavior suggest this may not be the case. The majority of NAcc neurons show increases in firing rate in response to a cocaine predictive cue;a similar majority of VP neurons display increases in firing rate in response to a food predictive cue. A GABAergic inverse relationship of NAcc-VP firing predicts predominant decreases in VP neuron firing in response to cocaine predictive cues. The direction, magnitude, and prevalence of VP subregional neurons during cocaine-seeking behaviors and cue-reactivity will be assessed and compared with previously as well as simultaneously recorded NAcc subregional neurons. Spike triggered averaging of simultaneously recorded NAcc and VP neurons will provide insight into behavior-induced firing patterns. Our preliminary results suggest that VP neurons encode cocaine self-administration behavior heterogenously. Since cocaine addiction is typified by cycles of binging and abstinence, and cues produce cravings, our examination of the neurophysiological correlates of cocaine-seeking and cue-reactivity under drug and abstinent conditions may enable insight into the disorder.